Edge gating from a nozzle of an injection molding apparatus through a number of edge gate seals is well known. A multi-cavity edge, or side, gated injection molding apparatus 100 is shown in FIG. 1 that is described in U.S. Pat. No. 5,494,433 to Gellert, issued Feb. 27, 1996, which is incorporated by reference herein in its entirety. Generally, the multi-cavity edge-gated injection molding apparatus 100 includes several nozzles 102, one of which is shown in FIG. 1, that are coupled to a hot runner manifold 118 to receive a melt stream of moldable material therefrom.
Each nozzle 102 is mounted in an opening 104 in a mold plate 106. Nozzle 102 includes a nozzle melt channel 108 for receiving the melt stream from a manifold melt channel 132 and delivering the melt stream to mold cavities 112 via mold gates 110. Nozzle 102 includes a nozzle heater 126 that is monitored and controlled by a thermocouple 128, and manifold 118 includes a manifold heater 130. Nozzle heater 126 and manifold heater 130 are provided to maintain the melt stream of moldable material within melt channels 108, 132, respectively, at a proper processing temperature.
Mold cavities 112 are formed between respective cavity inserts 154 and mold cores 156. Cavity insert 154 is disposed within mold plate 106 and includes seals 150 and cooling channels 152 there between. Each mold core 156 is held in place by a mold insert 158. Mold cavities 112 are uniformly distributed around nozzle 102 with each mold gate 110 extending through a gate insert 114 that is held in position by a gate insert retainer plate 122 and mold insert 158. Each mold gate 110 is aligned with a gate seal 116 that is threadably coupled to a downstream end of nozzle 102. As such, the location of gate seals 116 is generally fixed relative to mold plate 106.
As illustrated in FIG. 1, manifold 118 is a “floating” manifold that is positioned below a back plate 120 and coupled to nozzle 102 such that manifold 118 does not contact mold plate 106. This arrangement allows for thermal expansion of manifold 118 and nozzle 102 in an axial direction. In such an arrangement, requisite axial thermal expansion of manifold 118 is accommodated by having a sliding/telescopic arrangement between manifold 118 and a sprue bushing 124 fixed to back plate 120.
In an alternate configuration in which the manifold is fixed, axial thermal expansion may be accommodated by virtue of a telescoping connection within the nozzle itself, as shown for example in FIG. 2 and described in U.S. Pat. No. 7,179,081 to Sicilia et al., issued Feb. 20, 2007, which is incorporated by reference herein in its entirety. Generally, the edge-gated injection molding apparatus 200 includes a manifold 202 that is located between a mold plate 204, a sprue bushing 206 and a back plate 208. A disk 210 generally restricts movement of manifold 202 relative to mold plate 204 and back plate 208 to axially fix the position of manifold 202. As such during operation, manifold 202 is effectively prevented from flexing in a direction of the back plate due to thermal expansion.
A plurality of nozzles 212 are coupled to the manifold 202. Only one nozzle is shown for simplicity, however, it will be appreciated that in a typical injection molding apparatus a plurality of nozzles are generally connected to a single manifold.
The nozzle 212 is generally comprised of multiple component portions, namely a first nozzle portion 214 and a second nozzle portion 216 disposed in series between the manifold 202 and a mold cavity 218. The first nozzle portion 214 includes a nozzle head 220, which is located adjacent to and axially fixed relative to manifold outlet 222, and a second end 224. The second nozzle portion 216 includes a first end 226, and a second end 228 configured as an edge-gate nozzle. The second end of second nozzle portion 216 is generally axially fixed in a manner as described with reference to FIG. 1.
As nozzle head 220 of first nozzle portion 214 and second end 228 of second nozzle portion 216 are generally fixed, to accommodate axial thermal expansion, first nozzle portion 214 and second nozzle portion 216 are coupled by way of a telescoping connection 230. As shown, telescoping connection 230 is positioned between second end 224 and first end 226 of first nozzle portion 214 and second nozzle portion 216, respectively. In the embodiment shown, the telescoping connection is provided by way of an extension 232 provided on telescoping connection 230, which is in threaded engagement with first nozzle portion 214, that is slidably received in a corresponding bore 234 provided on second nozzle portion 216.
In the art of injection molding, where a mold includes the use of a core to shape an interior surface of a part, there exists a problem known as core shift. This problem occurs when a melt stream of moldable material is injected into a mold cavity containing a slender core, and the injection pressure required to fill the mold cavity causes the core to deflect resulting in molded products with a non-uniform wall thickness. In medical molding applications, such as pipette molding and syringe barrel molding, this uneven wall thickness will result in volumetric discrepancies between molded parts as well as an overall increase in the number of defect parts which do not conform to the tolerance requirements of the end user.